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Passive margins and their terminal collisions through Earth history Dwight Bradley U.S. Geological Survey Dwight Bradley U.S. Geological Survey

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Conclusions about passive margins Passive margins are not known before the Neoarchean As far back as the Neoarchean, most passive margins have ended their tenure by colliding with an arc Peaks in the passive margin population at 1900 Ma, 550 Ma, and today correspond to times of continental dispersal Lulls at Ma and 300 Ma correspond to known (Pangea) or inferred supercontinents Unexpectedly, the seven longest-lived margins are Precambrian. No evidence for short lifespans in Precambrian Age distribution of blueschists and foredeep magmatism attests to real secular change in style of arc-passive margin collision, but does not require a fundamentally different tectonic regime

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Karlstrom, 2005 Laurentian NE-trending Proterozoic accretionary provinces– one of the most voluminous accretionary orogens in Earth history

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Conclusions about passive margins Passive margins are not known before the Neoarchean As far back as the Neoarchean, most passive margins have ended their tenure by colliding with an arc Peaks in the passive margin population at 1900 Ma, 550 Ma, and today correspond to times of continental dispersal Lulls at Ma and 300 Ma correspond to known (Pangea) or inferred (Columbia) supercontinents Unexpectedly, the seven longest-lived margins are Precambrian. No evidence for short lifespans in Precambrian Age distribution of blueschists and foredeep magmatism attests to real secular change in style of arc-passive margin collision, but does not require a fundamentally different tectonic regime